Changes in stand structure affect the release of negative air ions by plant communities. However, it remains unclear whether canopy density promotes or weakens this effect, and the interaction mechanism between negative air ion concentration (NAIC) and environmental factors at different canopy densities. A 6-day field experiment was conducted in three representative coniferous forests and one non-forest land in Kanas National Nature Reserve, China. Pathway analysis and decision analysis were adopted to explore the impact of ten environmental factors, including airborne bacteria content (ABC), air oxygen content (AOC), particulate matter 2.5 concentration (PM2.5), particulate matter 10 concentration (PM10), light intensity (LI), ultraviolet radiation intensity (URI), temperature (T), relative humidity (RH), wind speed (V), and air pressure (AP) on NAIC at different canopy densities. We found that NAIC at different canopy densities was sorted as follows: high canopy density forest (3 060±176 ions/cm3) >middle canopy density forest (2 645±227 ions/cm3) >low canopy density forest (2 295±257 ions/cm3) >non-forest land (1 784±257 ions/cm3). In forest communities, with increasing canopy density, AOC, PM2.5, PM10, and RH showed a rising tendency, while ABC, LI, URI, T, and V were in reverse. NAIC in high canopy density forest was closely related to RH, ABC, AOC, and PM2.5; NAIC in middle canopy density forest was greatly affected by RH and URI; NAIC in low canopy density forest was strongly linked with RH, ABC, URI, and PM10; NAIC in non-forest land was strongly affected by RH, ABC, and T. RH was the paramount environmental factor affecting NAIC at different canopy densities, followed by ABC. Our study highlights the impact of canopy density on NAIC, brings new insights into NAIC drivers, and will aid in programming urban forests or green spaces that perform the ecological functions of improving air quality and increasing NAIC
